It is often necessary to inject chemicals into the completion string or tubing of a completed well. For example, it may be useful to inject chemicals into the completion tubing to combat well conditions such as corrosion, paraffin, scale, or hydrate build up in the completion tubing. Flow properties of well can be enhanced through the injection of foaming agents or gas. The injection of chemical is typically accomplished by means of an injection assembly comprised of a sub or mandrel having injection tubing and an injection valve that is pre-installed on the completion string. The desired chemical is then pumped into the completion string by means of a pump at the surface of the well through the injection assembly by means of the injection tubing and the injection valve.
Before chemical can be injected into the completion string it is necessary to test the connections of the injection assembly including the connections between the injection sub, injection tubing, the injection valve, and the completion string in order to insure their integrity. This is typically done after the injection assembly is made up in the completion string that is to be inserted into the well bore. Pressure testing is typically done by running a test tool, on wire line with pressure hose, into the internal diameter of the completion tubing or string. This test tool is an elongated shaft having a pack off device positioned at each end. The pack off device is intended to seal a segment of the completion string or injection sub with the injection port of the injection sub between each pack off device. Before testing is accomplished the pack off device at each end of the test tool must be packed off and sealed against the internal diameter of the completion tubing or string.
Once the test tool is packed off and sealed, pressure is applied through the test tool in the space between each pack off device to test the injection sub, the pressure check in the injection valve, and the connection between the injection sub and the injection valve. Testing is accomplished by placing the ends of the test tool across the injection port of the injection sub that has been attached to completion and pressured up to the desired test pressure. While pressure is maintained, the injection tubing can be pressured up, to test the control line, the injection valve, any pressure check valves, and the connection between the upper injection valve and the injection tubing. Pressure can also be applied through the injection sub and injection tubing to verify that the injection valve will open at a desired pressure for the injection of chemicals into the production string.
It should be noted that injection tubing is eliminated when annular injection systems are utilized but the use of the internal completion tubing pressure testing device as described is still typically used in completion strings having annular injection systems)
Often times it is desirable to include a pressure burst disk in the injection assembly to allow access to the completion string in the well bore at a future time. This access can be accomplished by increasing the pressure in the injection assembly to an amount sufficient to burst the disk and gain access to the completion string. If such a pre-set pressure burst disk is required in the injection assembly, the typical test procedure has to be modified to avoid damage to the pressure burst disk. Due to the design of the pressure burst disk, the manufacturers do not recommend to pressure up on the backside or low-pressure side of a disk. Doing so could cause deformation of the disk that may change its pre-set burst pressure. Consequently, when pressure burst disks are utilized in the injection assembly all components of the injection assembly cannot be tested by the typical methods.
To test the injection tubing or valve connection, a testable fitting or connector is sometimes utilized. Such a testable fitting or connector generally will incorporate two sealing ferrules. Pressure can be applied through an external port to test the area between the two sealing ferrules. This tests only the external area between the sealing ferrules. It does not test the injection sub, injection valve, injection tubing, or any internal flow paths.
The internal wire line test tool described above presents many risks and disadvantages. The internal wire line test tool can become stuck in the completion string, be blown out of completion string, or break the wire line can break allowing the pressure test tool to fall downhole. Another and perhaps more significant disadvantage is that the injection sub may be damaged by the pressure test causing it to come apart, possibly resulting in the production string falling downhole. Further, pressure testing on rig floor increases rig time resulting in higher costs. Elevated pressures at the surface from the testing equipment can expose service personnel to unwarranted dangers creating personnel safety concerns. Consequently, there is a need for an improved method and apparatus to test the injection sub, with injection valve pre-installed, prior to the time the sub assembly is made up in the completion string and inserted into the well bore in order to reduce the incidence of the aforementioned risks and disadvantages.